Islamabad, Pakistan (CNN) -- The Taliban claimed responsibility Monday for two explosions targeting a government building in Pakistan's tribal region, a Taliban leader said.

The blasts killed 50 people and injured at least 70 others, according to Shamas Ul Islam, a senior government official in Mohmand Agency.

Umar Khalid, head of the Pakistani Taliban in Mohmand Agency, said pamphlets had been distributed in the area 20 days ago warning members of peace committees or Lashkars (tribal militias) to abandon any efforts to join the government in fighting militants or face "consequences."

"We will continue to attack all pro-government officials and their supporters who try to join any peace committees or Lashkars," Khalid said.

The blasts occurred as government officials were about to meet with members of a volunteer militia group established to fight militants in the area, said Maqsood Amin, another senior government official in Mohmand Agency.

Among those killed in the blasts was Haji Kachkol Khan, a senior leader of the peace committeee, Islam said.

Amin said two suicide bombers were responsible for the blasts. One detonated inside the building and another outside the building's gate, he said.

The explosions occurred in the agency's headquarters of Ghalanai, Pakistan. A curfew has been imposed in Ghalanai as a preventive measure, Islam said.

The victims were taken to a local hospital after the blast, said Mohammad Zafar, a senior medical officer.

Monday's attacks were not the first time anti-Taliban and pro-government militias have been targeted in Pakistan. The attacks have been increasing over the past year, but Monday's was one of the deadliest attacks this year. A November 5 suicide attack targeting a mosque in Dera Adam Khel, where locals had formed an anti-Taliban militia, killed 67 people. In July, another suicide attack killed more than 100 people, also in Mohmand Agency.

Mohmand is one of seven semi-autonomous tribal agencies along the 1,500-mile border that Pakistan shares with Afghanistan.

The Pakistani military has been battling insurgents in the area for some time.

The attacks underscore that when locals decide to take a stand against the Taliban, there are sometimes deadly consequences. The Taliban usually warns locals against taking such actions, as they did in Monday's attacks. The Pakistani government has said that such suicide attacks are a sign that the Taliban is growing desperate and becoming more aware that Pakistanis are taking a stand against them.

In a statement, the U.S. Embassy in Pakistan condemned the attacks. "While details of these suicide attacks are still being verified, it is clear this vicious crime killed and wounded many innocent people," the statement said. "Our thoughts and sympathies are with the individuals and families affected by these inhumane acts."